The present invention relates to a top entry ball valve and a clamp therefor.
In conventional top entry ball valves, it is most common that the surfaces for receiving the valve seats on the brims of the valve ports at the high- and low-pressure sides of a valve chamber are tapered so as to allow a ball valve to fit snugly on the valve seat rings. These conventional top entry ball valves have a disadvantage that the optimum depth by which the ball valve is allowed to fit between the seat rings is limited within a narrow range. A ball valve fitting deeply requires too much torque. On the other hand, a ball valve fitting shallowly provides only imperfect sealing. It is difficult, therefore, to keep the operation efficiency and sealing performance in an ideal condition. It is also difficult to machine the tapered surfaces so as to provide satisfactory surface accuracy.
In another type of conventional top entry ball valve, in which the opposite surfaces for receiving the valve seats are parallel to each other, a valve seat ring assembly, which is a combination of a valve seat ring, a belleville spring and a valve seat ring holder, is provided at the high-pressure side so as to allow the ball valve to fit closely on the valve seat ring. The valve seat ring holder is screwed into the valve port at the high-pressure side so that an operator can turn the valve seat ring holder so as to move it toward and away from the ball valve. This type of conventional top entry ball valve has disadvantages in that it is intricate in construction since the valve body must be tapped and in that fine particles to be conveyed through the valve port are apt to stick to the tapped surface and thereby cause difficulties in the disassembly.